Information Bus: Description and Operation

COMMUNICATIONS NETWORK

The vehicle has 3 module communications network protocols:
- controller area network (CAN)
- standard corporate protocol (SCP) communications network
- international standards organization (ISO) 9141 communications network

The CAN has an unshielded, twisted pair cable, data bus plus circuit 1827 (WH/LG) and data bus minus circuit 1828 (PK/LG). The ISO 9141 communications network is a single wire communications network, circuit 70 (LB/WH). The SCP communications network is an unshielded, twisted pair cable, data bus plus circuit 915 (PK/LB) and data bus minus circuit 914 (TN/OG). All 3 communications networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one diagnostic tool to be able to diagnose and control any module on the 3 communications networks from one connector. The DLC can be found under the instrument panel between the steering column and the radio.

The CAN is a high speed communications network used for diagnostic communication. The CAN operates in a degraded mode with the severing of one of the bus wires. Communications also operate in a degraded mode if one of the bus wires is shorted to ground or voltage, or if some but not all termination resistors are lost.

The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communications network, the diagnostic tool must ask for all information; the modules cannot initiate communications. The ISO 9141 communications network does not function if the wire is shorted to ground or battery voltage. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module will fail.

The SCP communications network remains operational even with the severing of one of the bus wires. Communications also continue if one of the bus wires is shorted to ground or voltage, or if some but not all termination resistors are lost.